(A) Field of the Disclosure
The present disclosure relates to a semiconductor light-emitting device, and more particularly, to a semiconductor light-emitting device including a substrate having a plurality of protrusions configured to reflect light beams from a light-emitting structure at different angles so as to increase the light-extraction efficiency.
(B) Description of the Related Art
Semiconductor light-emitting devices such as light-emitting diodes (LED) have been widely used in traffic lights, vehicle electronics, LCD backing lights, and general illumination. In the light-emitting diode an n-type semiconductor layer, a light-emitting region and a p-type semiconductor layer are essentially made to grow on a substrate to form a layered structure, and the electrodes are formed on the p-type semiconductor layer and on the n-type semiconductor layer. Light is generated through the recombination of holes and electrons that have been injected through the semiconductor layers to the light-emitting region, and then emitted through a light transmitting electrode on the p-type semiconductor layer or from the substrate. The material used for preparing the visible light-emitting diode includes the III-V compound such as AlGaInP for green, yellow, orange or red light-emitting diodes, and GaN for blue or ultraviolet light-emitting diodes, wherein the GaN light-emitting diode is formed on the sapphire substrate.
Extracting the light beams generated by the light-emitting layer to the outside of the light-emitting device is one important issue to be improved in the semiconductor light-emitting device. Researchers use the transparent electrode in the conventional light-emitting device to prevent the upward light beams generated by the light-emitting layer from being blocked on the propagation path to the outside of the light-emitting device, or use the reflection layer to reflect the downward light beams generated by the light-emitting layer back to the top of the light-emitting device. However, in addition to the upward light beams and downward light beams, the light-emitting layer also emits light beams in other directions, and a portion of the light beams are reflected internally into the light-emitting device due to the total reflection effect. Consequently, the light beams may be adsorbed by the light-emitting layer, rather than propagate to the outside of the light-emitting device.
TW 561632 discloses a semiconductor light-emitting device having at least one recess and/or protruding portion created for scattering or diffracting light generated in a light-emitting region on the surface portion of a substrate. The recess and/or protruding portion has a shape that prevents crystal defects from occurring in semiconductor layers. In addition, TW 536841 discloses a semiconductor light-emitting element having an undulation formed on the surface of a first layer (substrate), and a second layer having a refractory index different from that of the first layer grown to fill the undulation. Furthermore, a first crystal may be grown in an undulated shape on a crystal layer, which is the foundation of crystal growth. After such undulated refractory interface is formed, a semiconductor crystal layer having a refractory index different from that of the first layer is laminated thereon.
US 20050179130 discloses a semiconductor light emitting element on a patterned substrate, wherein the substrate has at least one recess and/or protrusion formed on the surface thereof so as to scatter or diffract the light generated in an active layer. However, the sloped surfaces of the protrusion has notches, and it is well-known that the notches result in the generation of voids in the semiconductor layer formed by the epitaxy process on the protrusions, and the voids in the semiconductor layer affects the light-extraction efficiency.